Here is another great must have book for you!
It is the history of the PA Turnpike fully illustrated.
Gives the full history of the road including the additions and extensions even out beyond Pittsburg.
Also goes over all the tunnels that were originally supposed to be for the south penn rail line never completed.
Some of this info is readilly available from some great sites on the web but the photos in the book make it worth having.
Here are some examples
They also have one out on the Delaware river Brige (Ben Franklin) I'll have to pick up!
Heck the bridge in 
